1. Field of the Invention:
The present invention relates to a semiconductor device, as well as to the process for producing that semiconductor device.
2. Description of the Prior Art:
A semiconductor device of integrated type is referred to as a semiconductor integrated circuit (I.C.), wherein all of the circuit elements, i.e. such active elements as a bipolar transistor or a unipolar transistor, typically an MOS (metal-oxide-semiconductor) transistor, and such passive elements as a diffused resistor or capacitor, are formed on the surface of a semiconductor substrate. Since it is necessary to enhance the integration degree of the circuit elements, so as to produce the semiconductor integrated circuit at low cost, attempts have been made, in the formation of the circuit elements on the semiconductor substrate, to reduce the surface area of the circuit elements as small as possible. In addition, various arrangements of the circuit elements suited for a high density integrated circuit have been devised, in accordance with the kinds of the integrated circuit, by experts in the art. Furthermore, the kinds of the circuit elements suited for the high density integrated circuit are carefully selected. For example, in a static random-access memory, in which flip-flop circuits were constituted by means of MOS transistors, the all-transistor type memory cell was conventionally produced by utilizing the channel resistance of the MOS transistors for a resistance load of the memory cell, so that the integration degree of the random-access memory could be enhanced. Since the conventional diffused resistor had to be rather long, the channel resistance was used instead of the diffused resistor. However, in accordance with a recent development in the semiconductor industry, polycrystalline silicon layers having a high resistance can be reliably formed by a chemical vapor growth technique, so that layers having constant resistance can be repeatedly reproduced.
Research by the present inventors directed to replacing the MOS transistor used for the load of the memory cell with a resistor element made from the polycrystalline silicon having a high resistance, indicates the following requirements. Namely, the resistor element(s) must be isolated from the other elements and the wiring connecting various circuit elements of the memory cell, without reducing the integration degree thereof, while the resistor element(s) must be easily formed and precisely adjusted to a predetermined resistance value in the production of the memory cell.